becoming very worried about six year old daughter

When I was pregnant with my now six year old, I had a two vessel cord and they found at my 20 week sonogram that she had AV canal malformation (basically, her heart looked like a donut and she only had one large valve across the top of her heart instead of two.)
they said with the combination of these two things, she had a 70% chance of having Down's.

She does not have Down's, and before she was born, the bottom portion of the hole in her heart grew tissue which "closed" it, changing her heart defect to a "partial AV canal", "atrioventricular canal defect" or "ASD primum"

She had open heart surgery at 6 months old, and her heart has been doing great. when she was a little over a year old, she was diagnosed with hypothyroidism, which has very strangely become normal now.

She had some breathing issues (minor obstructive sleep apnea...had her tonsils and adnoids removed) and her pulmonary dr sent us to a genetic specialist, who spent not even five minutes with my daugther, who said "I think she has a connective tissue disorder...that's probably what caused her heart defect..follow up with your cardiologist" and blew us off.

Now, at age six, she is very active and plays at school and plays sports. For the past six months or so, her elbows and shoulders pop very loudly when she wakes up and she moans in pain. Now, she is also complaining of pain in her fingers, ankles and knees. They pop loudly and wake her up from her sleep, crying at times.

She is very flexible and has very soft skin (one of the concerns the pulmonary dr had at age one) and I am now worried that she may have Ehlers-Danlos syndrome or something like that.

I don't know what type of doctor I need to take her to. When I mentioned the concern to my pediatrician, he said he wasn't worried about it....but I am.

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